Add word wrap feature

Hi Jeff:

I'm using shinyAce for a project of mine and word wrapping would really be useful. I don't know a lick of javascript, but I was able to hack this together based on your existing code and the [ace how-to guide](http://ace.c9.io/#nav=howto). It seems to work well on my Mac. 

Please note that I haven't updated any documentation, since I'm running roxygen2 v4.0.0 and I can't seem to prevent it from rewriting all of your docs.

Comments/criticism welcome.

Cheers,
Nick